Exhaust note and tune?

Guys i first got a no tune S&B intake on my 08 GT. Car ran ok not to much different. Then i got an SCT X3 and used the 93 canned tune. Could not find my intake on the list and picked K&N since they were both no tune. Cars exhaust got much louder on throttle and it had good low end power. Then got a Brenspeed tune. 93 Perf. Car woke up with good throttle response but more power after 3K.
The thing is the exhaust note really mellowed out and the low end power seemed to be gone. What is the reasoning for all this? Anyone know?